RFR 8041565: JMX ObjectName could be refactored to save memory

Wed Aug 5 14:53:37 UTC 2015

I would remove the spec changes about the limit on the domain length,
which are a property of this particular implementation. It's perfectly
reasonable to blow up if the domain length is > 536,870,911, but
there's no reason for it to be in the spec.
Éamonn

2015-08-05 4:48 GMT-07:00 Jaroslav Bachorik <jaroslav.bachorik at oracle.com>:
> Eamonn, Daniel,
>
> thanks for the comments.
>
> I've updated the webrev to address them. Also, I've added a test to exercise
> the boolean flag en-/decoding in ObjectName.
>
> http://cr.openjdk.java.net/~jbachorik/8041565/webrev.03
>
>
> Cheers,
>
> -JB-
>
>
> On 4.8.2015 23:02, Daniel Fuchs wrote:
>>
>> Hi Jaroslav,
>>
>>   379      * This field encodes _domain_pattern, _property_list_pattern
>> and
>>   380      * _property_value_pattern booleans.
>>
>> If I'm not mistaken it also encodes the domain length.
>>
>>
>>   1072         if ((l & FLAG_MASK) > 0 ) {
>>
>> Although it is not expected that 'l' could be negative, it might be
>> better to write this test as:
>>
>>               if ((l & FLAG_MASK) != 0 ) {
>>
>> (+ I agree with Éamonn that l is not a great parameter name - nice to
>> see you back  Éamonn :-)) best regards, -- daniel On 8/4/15 4:20 PM,
>> Jaroslav Bachorik wrote:
>>>
>>> Hi, reviving this review. On 14.4.2015 16:58, Jaroslav Bachorik wrote:
>>>>
>>>> On 14.4.2015 14:56, Daniel Fuchs wrote:
>>>>>
>>>>> Hi Jaroslav, I like this change, but it does introduce an
>>>>> incompatibility, so it probably needs a CCC and some release notes.
>>>>> For instance, this test passes with the current version of
>>>>> ObjectName: public class StringLengthTest {      final static int
>>>>> smax = Short.MAX_VALUE;      final static int smore = smax + 126;
>>>>>      public static void main(String[] args) throws
>>>>> MalformedObjectNameException {          char[] chars = new
>>>>> char[smore];          Arrays.fill(chars, 0, smax, 'a');
>>>>> Arrays.fill(chars, smax, smore, 'b');
>>>>> System.out.println(new ObjectName(new String(chars), "type",
>>>>> "Test"));      } } I'm not sure what it will do with your changes :-)
>>>>
>>>> It will fail with assert (if enabled). Or truncate the domain name, I
>>>> suppose.
>>>>>
>>>>> With that in mind I believe you should consider throwing
>>>>> InternalError - or IllegalArgumentException - instead of using
>>>>> 'assert' statements.
>>>>
>>>> This would probably be better.
>>>>>
>>>>> BTW have you run the JCK?
>>>>
>>>> Yes. All passed. I don't think JCK is testing for unrealistic values
>>>> :) I don't see how one could come up with a domain name 32767
>>>> characters long.
>>>
>>> The proposed change has passed the CCC review. In case the domain name
>>> is longer than Integer.MAX_VALUE/4 a MalformedObjectNameException will
>>> be thrown. All the JMX tests and JCK are still passing.
>>> http://cr.openjdk.java.net/~jbachorik/8041565/webrev.02 -JB-
>>>>
>>>> -JB-
>>>>>
>>>>> best regards, -- daniel On 13/04/15 17:07, Jaroslav Bachorik wrote:
>>>>>>
>>>>>> Hi Roger, On 13.4.2015 16:07, Roger Riggs wrote:
>>>>>>>
>>>>>>> Hi Jaroslav, Minor comments: 1488+:  In forms like:
>>>>>>> _pattern_flag &= (~PROPLIST_PATTERN & 0xff);" The &0xff seems
>>>>>>> unnecessary since the store is to a byte field.
>>>>>>
>>>>>> Fixed: http://cr.openjdk.java.net/~jbachorik/8041565/webrev.01
>>>>>>>
>>>>>>> 1644:  the ? and : operators should be surrounded by spaces. There
>>>>>>> are other style issues, such as then statements on the same line
>>>>>>> as the 'if' but that may be beyond the scope of this change.
>>>>>>
>>>>>> I know but these style issue have been around since the file was
>>>>>> first committed. I didn't address them because it didn't feel right
>>>>>> to mix style changes with the actual functionality. Cheers, -JB-
>>>>>>>
>>>>>>> Otherwise looks fine  (as a 9 reviewer, but not specifically a
>>>>>>> serviceability reviewer). Thanks, Roger On 4/13/2015 5:43 AM,
>>>>>>> Jaroslav Bachorik wrote:
>>>>>>>>
>>>>>>>> Please, review the following change Issue :
>>>>>>>> https://bugs.openjdk.java.net/browse/JDK-8041565 Webrev:
>>>>>>>> http://cr.openjdk.java.net/~jbachorik/8041565/webrev.00 In
>>>>>>>> situations when there are 10s of thousands ObjectNname instances
>>>>>>>> around (enterprise setups etc.) the 3 separate internal boolean
>>>>>>>> fields can lead to a noticeable memory waste. Adding insult to
>>>>>>>> the injury, with the current field layout it is necessary to
>>>>>>>> align the instances by 4 bytes. When using JOL
>>>>>>>> (http://openjdk.java.net/projects/code-tools/jol/) to inspect the
>>>>>>>> object layout we can see this: Before optimization (JDK8u40): ---
>>>>>>>> javax.management.ObjectName object internals: OFFSET SIZE TYPE
>>>>>>>> DESCRIPTION VALUE       0 12 (object header)| N/A      12 4 int
>>>>>>>> ObjectName._domain_length N/A      16 1 boolean
>>>>>>>> ObjectName._domain_pattern N/A      17 1 boolean
>>>>>>>> ObjectName._property_list_pattern N/A      18 1 boolean
>>>>>>>> ObjectName._property_value_pattern N/A      19 1
>>>>>>>> (alignment/padding gap) N/A      20 4 String
>>>>>>>> ObjectName._canonicalName N/A      24 4 Property[]
>>>>>>>> ObjectName._kp_array N/A      28 4 Property[]
>>>>>>>> ObjectName._ca_array N/A      32 4 Map ObjectName._propertyList
>>>>>>>> N/A      36 4 (loss due to the next object alignment) Instance
>>>>>>>> size: 40 bytes (estimated, the sample instance is not available)
>>>>>>>> Space losses: 1 bytes internal + 4 bytes external = 5 bytes total
>>>>>>>> {noformat} After optimization (JDK9 internal build): ---
>>>>>>>> javax.management.ObjectName object internals:  OFFSET SIZE TYPE
>>>>>>>> DESCRIPTION VALUE       0 12 (object header) N/A      12 2 short
>>>>>>>> ObjectName._domain_length N/A      14 1 byte
>>>>>>>> ObjectName._pattern_flag N/A      15 1 (alignment/padding gap)
>>>>>>>> N/A      16 4 String ObjectName._canonicalName N/A      20 4
>>>>>>>> Property[] ObjectName._kp_array N/A      24 4 Property[]
>>>>>>>> ObjectName._ca_array N/A      28 4 Map ObjectName._propertyList
>>>>>>>> N/A Instance size: 32 bytes (estimated, the sample instance is
>>>>>>>> not available) Space losses: 1 bytes internal + 0 bytes external
>>>>>>>> = 1 bytes total After optimization we can save 8 bytes per
>>>>>>>> instance which can translate to very interesting numbers on large
>>>>>>>> installations. To achieve this the domain name length is set to
>>>>>>>> be *short* instead of *int* and the three booleans kept for the
>>>>>>>> performance purposes are encoded into one byte value (as proposed
>>>>>>>> by the reporter, Jean-Francois Denise). All the regression and
>>>>>>>> JCK tests are passing after this change. Thanks, -JB-
>
>